A division of the US Department of Health and Human Services has finalized health risk levels for four per- and polyfluoroalkyl substances (PFAS). PFAS are valuable as manufacturing aids and in consumer products for properties such as resistance to heat, stains, and water. But those properties also mean that they are environmentally persistent, and several have been linked to cancer and other health problems. The Agency for Toxic Substances and Disease Registry (ATSDR) says the minimal risk level for perfluorooctanoic acid (PFOA) is 3 × 10–6 mg per kilogram of body weight per day, while the level for perfluorooctanesulfonic acid (PFOS) is 2 × 10–6 mg per kilogram of body weight per day. Those levels are an order of magnitude lower than the Environmental Protection Agency’s advisory safe daily dose levels. For two other substances evaluated by the ATSDR, perfluorohexanesulfonic acid (PFHxS) and perfluorononanoic acid (PFNA), the EPA does not have safe daily dose levels. The ATSDR report has been in the works since 2009 and adheres to draft levels released in 2018. The EPA is working on setting enforceable regulatory limits for PFOA and PFOS in drinking water.